In industrial processes, such as the manufacture of semiconductor devices, commercial inert gases are used. These inert gases have traces of impurities which must be removed during the industrial process. Inert gas purifiers are known which use impurity gas sorbing materials such as xe2x80x9cgettersxe2x80x9d to remove the impurities.
For example, U.S. Pat. No. 6,013,195 to Corazza et al., U.S. Pat. No. 5,961,750 to Boffito et al. and U.S. Pat. No. 4,996,002 to Sandrock et al. provide examples of gas sorbing materials. Specifically, U.S. Pat. No. 6,013,195 to Corazza et al. describes getter materials capable of being activated at low temperatures. The patent describes compositions including a getter component having Zr, V and Fe and an activator component. U.S. Pat. No. 5,961,750 describes nonevaporable getter alloys containing Zr, Co, and a third component. Additionally, U.S. Pat. No. 4,996,002 provides a method of manufacturing tough porous getters, of high Zr-content Zrxe2x80x94V alloys that have minor additions of elements such as Fe, Ni, Mn and/or Al. Getter materials are used in conjunction with gas purifiers.
A typical gas purifier is described in U.S. Pat. No. 5,172,066 to Succi et al. The purifier has an impure gas inlet in fluid communication with a housing that contains a gas sorbing material or getter materials. The housing is also in fluid communication with a gas outlet through which purified gas passes. A resistance heater wrapped around the housing maintains the temperature within the cylinder at 400xc2x0 C. The gas purifier housing in this patent is described as being in the form of a stainless steel cylinder. A disadvantage in using a gas purifier having a simple cylindrical housing is that the cylinder does not provide a sufficient gas residence time within it for optimal removal/retention of impurities.
U.S. Pat. No. 5,238,469 to Briesacher et al. describes a gas purification system for the purification of noble gases and nitrogen. Here, as above, an impure gas is heated within a cylindrical housing and the impure gas is contacted with an impurity sorbing material for removing impurities and producing a purified gas. Additionally, it is described that the purified gas is cooled to a temperature of less than about 100xc2x0 C. and then contacted with a hydrogen sorbing material to remove residual hydrogen. Preferably, in the prior art, the hydrogen sorbing material is used at temperatures ranging from ambient temperature to about 40xc2x0 C. The patent describes two types of heat exchangers for cooling the purified gas.
Both coiled heat exchangers and parallel tube heat exchangers are described. The heat exchangers are described as being located within a vessel separate from the cylindrical housing, however, it is known in the art that the heat exchanger may be located within the same housing as the heater. Disadvantages of the external coiled heat exchangers, as described in the patent, are that they are bulky and energy draining. Additionally, the coiling of the exchanger can interfere with the finished surface causing production of particulates by the coil itself.
Furthermore, in the prior art, high performance filters are known to be used in conjunction with the gas purification process. These filters are used at ambient temperatures. On contact with the ambient temperatures, the filters tend to trap moisture leading to contamination.
Therefore, it is an object of the present invention to provide an improved apparatus for thermal management for use in a gas purification process at least by 1) increasing the residence time of the gas within the apparatus in order to optimize the purification efficiency, 2) decreasing the amount of energy used in the process and 3) decreasing the amount of contamination produced by the apparatus.
The invention provides an improved apparatus for thermal management in a gas purification process. The apparatus of the present invention includes a two section purifier wherein the two sections are joined in a unitary vessel. A feature of the present invention is a single continuous serpentine shape that makes up the unitary purifier vessel. The continuous serpentine shape provides the vessel with an aspect ratio such that the vessel may provide optimal conditions for the retention/removal of impurities within a gas. The serpentine shape also allows for increased residence time of the gas within the purifier, therefore, increasing the purification efficiency. The purifier vessel has a primary section that is separated from a secondary section by a Joule-Thomson cooling device, another feature of the present invention.
As is known in the art, during a first stage of the gas purification process, a heater assembly coupled to the purifier vessel heats an impure gas, such as a noble gas. The heated impure gas enters the purifier vessel by way of a purifier inlet. Alternatively, the heating assembly may be eliminated and the gas may be heated within the vessel. Within the purifier vessel is an impurity gas sorbing material such as getters or getter xe2x80x9cpillsxe2x80x9d. The getters are heated to an optimal temperature usually, 400-450xc2x0 C. At this temperature the getters become active as a chemical pump. Typical impurities within a noble gas include O2, H2O, CO, CO2, H2, N2 and CH4. These impurities react with the surface area of the getter pills to form solid compounds. These compounds are primarily oxides, carbides and nitrides of the base getter material, which is for example Zr2O3 Hydrides are also formed and are contained within the bulk of the getter pills in the form of a solid solution. Hydrogen may escape from the hydride formed as well as from the surfaces of the gas purifier in the heated primary section of the vessel. Therefore, a xe2x80x9ccool zonexe2x80x9d within the secondary section of the purifier vessel is required to capture the released hydrogen. In the prior art the cool zone is known to be within the range of less than 100xc2x0 C. to ambient temperatures.
A further feature of the invention is the Joule-Thomson cooling device, dividing the primary section of the purifier vessel from the secondary section and providing a temperature range of approximately less than 200xc2x0 C. and greater than about 100xc2x0 C. within the secondary section of the vessel. The Joule-Thomson cooler is known in the art, however, it is not known to be used in conjunction with inert gas purifiers. The Joule-Thomson cooler causes gas pressurization in the primary section of the vessel, and gas expansion or cooling after the gas flows from the primary section to the secondary section.
Coupled to the secondary section of the purifier vessel is a further feature of the invention. Within the secondary section of the vessel, near a purifier vessel outlet, a sintered metal high performance particle filter is found. High performance particle filters are known in the art, however, are not known to be located at the outlet end of a purifier vessel of a gas purifying device where they are heated, as is provided in the present invention.